How to pick a book in Spanish: discussion

I've finally reached the point where I am starting to feel comfortable reading in Spanish. I'm using the Kindle, so I can look up words, and I picked a book I know pretty well so I don't get too lost.

I used to teach second and third grade, the point at which kids are usually transitioning from easy picture books to independently tackling chapter books and longer reads. I definitely feel like a transitional reader myself!

Those of you who have started to read books in Spanish, what are your tips for picking a book?

In class, we sometimes used the rule of thumb of "no more than 10 words per page that you don't understand," largely because more than that can get pretty exhausting. Of course, every kid had their own tolerance of unknown words. Some kids were most enthusiastic about books with pictures, because those helped keep them from getting lost. Graphic novels are pretty great for that, and books that were also movies were similarly familiar.

Harry Potter is definitely not a "transitional" book for the average third grader, but it works well for me as an adult. As I said, I'm already familiar with the plot, and my English vocabulary is strong enough to support me through sophisticated word choice. I've seen warnings about Harry Potter not teaching you "useful" Spanish, because you're unlikely to encounter wands, goblins, or charms in real life. But I'm getting lots of Muggle vocabulary too, and practicing sentence structure. The dialogue probably still leans British, but my Spanish teacher is a Spaniard who just moved to the States from England, so I'm already getting that. Anyway, I don't know that I'd recommend Harry Potter to someone who wasn't already a fan, but I do recommend it to fans!